DataModels + Appv2 migration : OK

module/applications/sheets/base-item-sheet.mjs

@@ -25,6 +25,13 @@ export default class BoLBaseItemSheet extends HandlebarsApplicationMixin(foundry
     window: {
       resizable: true,
     },
+    tabs: [
+      {
+        navSelector: 'nav[data-group="primary"]',
+        contentSelector: "section.sheet-body",
+        initial: "description",
+      },
+    ],
     actions: {
       editImage: BoLBaseItemSheet.#onEditImage,
       postItem: BoLBaseItemSheet.#onPostItem,
@@ -146,29 +153,34 @@ export default class BoLBaseItemSheet extends HandlebarsApplicationMixin(foundry
   }
 
   /**
-   * Activate tab navigation
+   * Activate tab navigation via CSS only (no re-render) to preserve unsaved form state.
    * @private
    */
   _activateTabs() {
-    const nav = this.element.querySelector('nav.tabs[data-group="primary"]')
+    const nav = this.element.querySelector('nav[data-group="primary"]')
     if (!nav) return
+    const section = this.element.querySelector('section.sheet-body')
+    if (!section) return
 
     const activeTab = this.tabGroups.primary || "description"
-    
-    // Activate tab links
+
+    // Set initial active state
     nav.querySelectorAll('[data-tab]').forEach(link => {
-      const tab = link.dataset.tab
-      link.classList.toggle('active', tab === activeTab)
-      link.addEventListener('click', (event) => {
-        event.preventDefault()
-        this.tabGroups.primary = tab
-        this.render()
-      })
+      link.classList.toggle('active', link.dataset.tab === activeTab)
+    })
+    section.querySelectorAll('[data-tab]').forEach(content => {
+      content.classList.toggle('active', content.dataset.tab === activeTab)
     })
 
-    // Show/hide tab content
-    this.element.querySelectorAll('.tab[data-tab]').forEach(content => {
-      content.classList.toggle('active', content.dataset.tab === activeTab)
+    // Tab click — CSS-only switch, no render()
+    nav.querySelectorAll('[data-tab]').forEach(link => {
+      link.addEventListener('click', (event) => {
+        event.preventDefault()
+        const tab = link.dataset.tab
+        this.tabGroups.primary = tab
+        nav.querySelectorAll('[data-tab]').forEach(l => l.classList.toggle('active', l.dataset.tab === tab))
+        section.querySelectorAll('[data-tab]').forEach(c => c.classList.toggle('active', c.dataset.tab === tab))
+      })
     })
   }